Hydraulic pump or motor

ABSTRACT

An hydraulic pump or motor and, more particularly, a low-speed high-torque motor wherein radial forces are balanced by symmetrically opposed ball piston elements and there is a constant mechanical torque output or input throughout every revolution of the pump or motor and further having a construction including first and second casing parts, one of which mounts the cylinder block carrying the ball pistons and the other of which mounts a power shaft and with a sliding coupling between said shaft and cylinder block whereby assembly is facilitated and the cylinder block is free to adjust on its mounting as required for the ball pistons to follow the annular race coacting with the ball pistons.

United States Patent Siesennop et a1.

[451 Oct. 3, 1972 [s41 HYDRAULIC PUMP OR MOTOR I Wis.

[73] Assignee: Rex Chainbelt Inc.

[22] Filed: Jan. 20, 1970 [21] Appl. N0.: 4,270

[52] US. Cl ..91/498 [51] Int. Cl ..F01b 13/06 [58] Field of Search ..91/491, 497, 498

[56] References Cited UNITED STATES PATENTS 2,712,794 7/1955 I-Iumphreys ..91/485 2,101,829 12/1937 Benedek ..91/498 2,772,755 12/1956 Nallinger et a1. ..91/498 2,882,831 4/1959 Dannevig ..91/498 2,992,619 7/1961 Nilges ..91/498 3,078,808 2/1963 Byers, .Ir ..91/491 459,735 9/1891 Benham ..91/498 2,547,645 4/1951 Horton ..91/498 3,046,950 7/1962 Smith ..91/504 3,187,681 6/1965 Firth et a1. ..91/498 3,287,993 1 1/1966 Lomnicki ..91/498 FOREIGN PATENTS OR APPLICATIONS 515,422 12/1939 Great Britain ..91/498 578,392 5/1945 Great Britain .91/497 579,904 Great Britain ..91/497 Primary Examiner--William L. Freeh Attorney-Hofgren, Wegner, Allen, Stellman' & Mc- Cord [57] ABSTRACT An hydraulic pump or motor and, more particularly, a low-speed high-torque motor wherein radial forces are balanced by symmetrically opposed ball piston elements and there is a constant mechanical torque output or input throughout every revolution of the pump or motor and further having a construction including first and second casing parts, one of which mounts the cylinder block carrying the ball pistons and the other of which mounts a power shaft and with a sliding coupling between said shaft and cylinder block whereby assembly is facilitated and the cylinder block is free to adjust on its mounting as required for the ball pistons to follow the annular race coacting with the ball pistons.

2 Claims, 5 Drawing Figures PATENTEnncra I972 3.695.147

sum 1 or a fn/eniors HYDRAULIC PUMP R MOTOR BACKGROUND OF THE INVENTION This invention pertains to a ball piston pumpor motor which can function as a low-speed high-torque motor having a constant mechanical torque output with radial balancing of forces by symmetrically opposed ball pistons or as a pump demanding a constant mechanical torque input as provided by a relation between the number of ball pistons and lobes'of acamv formed on an annular race surrounding the ball pistons and with the contour of the. cambeing. constructed to provide optimum machinability with thev desired. zero torque ripple characteristics and particularly with such cam providing a cycloidal motion to reduce ball acceleration for the ball pistons, which reduces Hertz stresses on the annular race and which hasa constant. fluid flow demand to cut down transients in the fluid:

system and which provides substantially zero torque ripple over the entire operating speed range of the mo-' tor.

Prior art known to the applicants includes Taylor US. Pat. No. 137,261 relating to a rotary steam engine wherein a series of pistons are. operated in chambers and the position thereof is controlled by a. cam. The

cam contour controlling the pistons isreferredto as. in

cluding sections which are struck as arcs of circles and with these sections being connectedv by inclined. faces having a cycloidal curve. Such a constructionembodying a blending of curves provides discontinuities where. each of the two curves having different slopes. meet, which results in excessive l-lertzstresses and can cause surface failures in the cam. Additionally, the contours disclosed in the Taylor patent may be suitable. for

steam, which is expansible; however, the arrangement of curves would not provide themaximum capacity in a minimum size for a hydraulic device, as provided'by the structure disclosed herein.

The Dannevig US. Pat., No. 2,882,831, discloses an hydraulic pump or motor which is alleged. to have. substantially no pulsation or ripple. in the output. The patent discloses varying numbers of ball pistons. and lobes associated therewith and with total discharge. being shown as constant. The patent describes constant acceleration and deceleration. sections which provide the displacement diagram shown in the patent. How ever, such a cam for controlling the ball pistons has abrupt changes of acceleration and such changes produce noise, vibration and wear. Such' aconstruction is believed practical only at lower speeds of'operation. Additionally, the constructions disclosed in the patent. do not provide complete balancing of radial; forces.

SUMMARY ing part rotatably mountinga power shaft and with the casing parts in assembled relation with an annular race therebetween having a cam to control the positioning of the ball pistons, the power shaft and cylinder block are. interconnected by a sliding coupling which permits simple interfitting and less critical alignment when the casing parts are assembled and which further permits adjustment of the cylinder block as required to permit seatingof the ball pistons in a contour of the race cam.

The race more particularly has a cycloidal curve cam contour providing a series of lobes, each of which defines an. effective dwell for a ball piston. An effective. dwell is a length of cam whereinthere is relatively littledisplacement. For brevity, such' an effective dwell will. hereinafter be referred to simply as a dwell." There are dwells intermediate said lobes and with porting'inthe pintlearranged in association with the chambers for the ball piston in the cylinder block to have a chamber open toan inlet port while. a ball piston is on a lobe and with a transition between an inlet port and an outlet port at a dwell intermediate the lobes and wherein the dwells are defined by connected cycloidal curve sections having a characteristicof imparting substantially zero velocity to the ball pistons.

The rise of the cycloidal curve cam between dwells imparts a sinusoidal or harmonicacceleration to a ball piston having both positive and negative accelerations which over-all provide a gradually increasing velocity to the ball piston reaching a maximum at the mid-point of the. rise between dwells followed by a symmetrically decreasing velocity to the dwell at the end of the rise. This velocity curve corresponds-to the torque output of each ball. piston in a motor unit and with certain combinations of ball pistons and lobes of a cycloidal cam the torque is substantially constant throughout the entirerevolution of the device.

Investigation has shown that only a limited number of combinations of'balll pistons and lobes of a cycloidal curve cam will provide a constant torque output including. units having eight balls and six lobes, eight balls and two. lobes, 12. balls and three lobes, or 121 balls and two lobes. Additionally, such units have balanced radial forces by diametrically opposed. pistons.

An object of this invention is to provide a new and improved fluid translating device, such as a pump or motor, havinga rotatable cylinder block with a plurality of ball pistons, the position of 'which is controlled by an annular raceconcentric with the cylinder block and having a cycloidal curve cam contour which can be easily machined and which provides smooth velocity transitions between adjacent sections of the cycloidal camandwithout discontinuities in the surface-to avoid greatly stressing the cam surface.

Anotherobject of theinvention is to provide a device as definedinthe preceding paragraph wherein the cam contour provides dwells related to the porting for the ballpistons to communicate-with: the porting while the ball pistons are on the dwells where the velocity imparted to the ball pistons is substantially zero and torquevariations are substantially avoided upon initial communication of the ball piston with the port and wherein gradual acceleration of the ball piston occurs as it moves along the rise of the cam withlow velocities and low maximum accelerations to minimize vibration, wear, noise and'shock.

Still another object is to provide a device as defined in the preceding paragraphs wherein transient fluid pressures are avoided, with constant fluid flow to provide substantially constant torque input or output.

An additional object of the invention is to provide a fluid translating device as defined in the preceding paragraphs wherein the device is constructed of two primary casing parts, one of which has a pintle rotatably and loosely mounting the cylinder block carrying the ball pistons and the other part rotatably mounts the power shaft and with a sliding coupling therebetween which can be interfitted on assembly of the two casing parts together with the annular race mounted therebetween and which permits eccentric adjustment of the cylinder block relative to its mounting pintle as required for seating of the ball pistons in a transverse recess formed in the annular race cam.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical central section, taken from front to rear of the fluid translating device, and generally along the line 11 in FIG. 2;

FIG. 2 is a vertical transverse section, taken generally along the line 22 in FIG. 1;

FIG. 3 is a diagram showing the torque of each ball piston in one reciprocating cycle thereof and the overall total torque;

FIG. 4 is a fragmentary view of a section of the cam track and a ball in association therewith; and

FIG. 5 is a diagram showing the acceleration, velocity, and displacement characteristics of a ball piston during one-half of a complete reciprocation thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENT The fluid translating device, as shown in FIG. 1, has a first casing part associated with a second casing part 11 and having an annular race 12 captured therebetween. A power shaft 15 extends outwardly of the second casing part 11. The device can be used as either a pump or motor and when used as a motor the power shaft 15 is an output shaft, while when the device is used as a pump the power shaft 15 is an input shaft and the fluid connections to the device are made dependent upon its mode of operation. For purpose of description, the device will be described as a motor with such motor having low-speed high-torque characteristics.

The first casing part 10 has a pintle 16 formed integrally therewith which rotatably mounts a cylinder block 17 having a series of equally spaced, radially extending chambers 18 each of which mounts a ball piston 19. Each ball piston 19 is urged outwardly of its chamber by a spring engaging between an internal wall 26 in the chamber and a movable shoe 27 which has a central opening in which the ball piston 19 is seated. Each of the chambers 18 is open-ended, with an opening 30 at the inner end which communicates alternately with fluid inlet and outlet ports equally spaced apart about the surface of the pintle 16. An inlet port 31, which is a pressure port for the motor, is shown in association with the opening 30 in FIG. 1, with the inlet port being supplied by connection to an annular groove 32 in the pintle, which is supplied with hydraulie fluid under pressure from a port plate 35 fastened to an outer face of the first casing part 10.

An outlet port 36 communicates with a second annu-' lar groove 37 in the pintle 16 which connects to lines external of the motor through connections to the port plate 35.

The ball pistons 19 coact with a cam surface 40 on the inner face of the annular race 12, with this cam being transversely recessed, as indicated at 41, to have the ball pistons partially seated and provide increased contact between the ball pistons and the cam. The cylinder block 17 is loosely mounted on the pintle 16 to permit movement of the block on the pintle whereby the ball pistons can fully seat in the transverse recess 41 of the cam. This mounting is provided by a difference between the external diameter of the pintle l6 and the internal diameter of the block 17, which is greater than an accumulation of tolerances along with space for movement lengthwise of the pintle as defined by the mounting of the block by a pair of thrust washers 45 and 46 positioned at either side of the cylinder block and with this assembly held in position by a retaining ring 47.

This freedom of movement of the cylinder block 17 to permit the ball pistons to center in the race recesses, which also helps to prevent polarization of the ball pistons, is further facilitated by the nonrigid connection between the cylinder block and the power shaft 15. This connection is made by a coupling which facilitates assembly of the device and which permits eccentricities between the cylinder block and the power shaft. The power shaft 15 is rotatably mounted in the second casing part 1] by bearings, indicated generally at 50, having the outer races held in position by a retaining ring 51 fastened to the interior of the second casing part and with a seal retaining flange 52 fastened to the outer face of the casing part and enclosing the power shaft 15. A lock unit, indicated generally at 53, holds the inner races on the power shaft 15. An inner, generally rectangularly shaped end 55 of the power shaft is fitted into an opening 56 in a coupling plate having ends 57 and 58 extending outwardly to interfit with pairs of cars formed integrally with and extending outwardly from a side face of the cylinder block. The end 57 of. the plate fits between a first pair of ears with one of said ears being indicated at 59, while the end 58 of the bar fits between a pair of ears, with one of the ears being indicated at 60 whereby a floating coupling is provided.

With the construction described above, the power shaft can be assembled in the second casing part 11, while the cylinder block and associated elements can be mounted on the pintle 16. The annular race 12 is then positioned between the casing parts and concen trically with the pintle 16. The coupling plate has its ends fitted between the pairs of ears to operatively connect the cylinder block 17 to the power shaft 15 without requiring exact alignment between these parts and permitting shifting of the cylinder block 17 during operation of the device. The casing parts and annular race 12 are held in assembled relation by a series of tie providing for balance of radial forces and for substantially constant mechanical torque output or input throughout every shaft revolution of the device, with resultant substantially zero torque ripple, including down to very low speeds and to a speed of less than 1 rpm.

The cam 40 provided on the annular race 12 is constructed as a cycloidal curve having a series of lobes with the lobes 70-75 being identified in FIG. 2 for the six-lobe cam. This six-lobe cam is associated with an eight ball piston arrangement wherein the ball pistons 19 are more particularly identified by reference numerals 19 and 19a through 19g. Each of the lobes 70 75 defines a dwell wherein the ball piston engaging said dwell is at its innermost position as shown for th'eball pistons 19b and 19f in FIG. 2. Intermediate the dwells defined by the lobes are a second series of dwells 80- 85 which define an outermost position for ball pistons, as shown for the ball pistons 19 and 19d in FIG. 2. Intermediate each of the dwells is arise, with arise 90 extending between dwells 70 and 80 and a'rise 91 extending between dwells 71 and 80 and with corresponding rises extending between succeeding dwells around the periphery of the cam.

A ball piston 19 goes through an entire reciprocating cycle in moving between dwells 70 and 71, with this being through a rotational arc of 60, with thesix-lobe cam shown in FIG. 2.

A portion of the cam 40 isshown laid out in FIG. 4 wherein a ball piston 19 has moved approximately from the center of the dwell 70 and is moving outwardly along the rise 90 of the cam.

The cycloidal curve cam 40 provides desirable characteristics for the ball pistons contributing to constant torque input and output in addition to being a cam which is readily machinable and which can 'be of reasonable size. These characteristics are shown in the diagram of FIG. 5 wherein the X-axis has the angle of rotation or cam angle of the cylinder block indicated with a 30 angle covering the movement of a ball piston 19 from a lobe dwell 70 to a dwell '80 and being onehalf of a complete reciprocating cycle of a ball piston. The curve 100 in the diagram of FIG. 5 shows the displacement of the ball piston 19 with the dwells occurring at 70 and 80 being at the ends of the curve '100. During this displacement stroke, the acceleration'of the ball piston 19 is a sinusoidal or harmonic motion, as shown by the line 101 and changes from a positive acceleration to a negative acceleration at the mid-point of the stroke and which results in a velocity curve indicated by the line 102. The acceleration is zero at each of the dwell positions of the ball piston and these dwell positions are related to the inlet ports 31 andthe outlet ports 36 formed in the pintle 16, as shown particularly in FIG. 2. Assuming counterclockwise rotation of the cylinder block 17 in FIG. 2 and noting particularly the ball piston 19f, the ball piston is on the dwell 72 and is at the point of having its chamber inner end 30 opening into communication with the inlet port 31 while having just closed communication with the outlet port 36. This transition occurs without any discontinuity in the cam surface because the adjacent cycloidal cam sections have the same slope which substantially lowers Hertz stress which would occur upon a discontinuity in the surface. Further, the acceleration of the ball piston is zero and there can only be at most a finite jerk and zero acceleration which translates into known properties for the device. Further, the acceleration curve 101 shows a gradual acceleration with a relatively low maximum acceleration, while the displacement curve, line 100, shows that there is an adequate extentof dwell to permit connection and disconnection to the ports while still'requiring only minimal rotational displacement before the ball piston commences linear displacement for doing work. With the openingand closing of the porting at the dwells there is very little pressure angle resulting from the forces applied to the ball piston and reacting against the cylinder block to minimize any modification of the torque output of the motor.

The velocity curve 102 translates into a torque pattern, shown in FIG. 3, wherein each of the ball pistons in moving through a rotational arc of provides a torque and wherein the sum of the torques provides a constant total torque, asshown in the diagram.

The torque provided by any ball piston is the force that the ball piston causes on the wall of the cylinder block chamber at a particular rotational angle times the distance of the ball piston from the center of the cylinder block at that particular angle and the construction disclosed herein provides a constant torque by having the sum of all the individual ball piston torques constant at all times and at all speeds of operation throughout the operating range of the device and with the porting in the cylinder block being sufficient to satisfy the full range of the velocity curve 102 of the cycloidal curve cam to have the torque curve for each ball piston match the velocity curve.

We have discovered that there are a number of combinations of ball pistons and lobes for a cycloidal curve cam which will provide constant mechanical torque output'or input, with one of these combinations being the eight ball piston and six lobe cam disclosed herein and another combinationis eight ball pistons and a two lobe cam. Additionally, a unit having twelve ball pistons and either a three lobe or two lobe cycloidal cam will 'provide'constant torque output or input and with radial'force balance.

We claim:

1. A low-speed high-torque motor having a casing with a pintle rotatably mounting a cylinder block, said block having eight equally spaced radially extending open-ended chambers, a ball piston in each of said chambers, an annular race fixed to said casing concentrio with said pintle and having a cam track with six equally spaced lobes'for cycling said ball pistons in said chambers during each'revolution of said cylinder block and with balance of radial forcesQa series of six equally spacedpressure ports in said block for communication with the inner ends of said chambers and a series of six equally spaced outlet ports each disposed between a pair of pressure ports, a power shaft operatively connected to said cylinder block, said cam being contoured to provide a cycloidal motion for each ball piston throughout the entire revolution of said cylinder block by having a series of cycloidal curves connected one to another to provide a dwell at each lobe where a ball piston initially communicates with a pressure port and has zero acceleration and a succeeding dwell halfway between lobes where transition occurs between communication with a pressure port to communication pennit rocking adjustment of said cylinder block and enable centering of the ball pistons in the cam track recess.

2. A low-speed high-torque motor as defined in claim 1 including a sliding coupling between the power shaft and cylinder block constructed to permit movement of the cylinder block radially of the power shaft to facilitate adjustment of the cylinder block for said centering of the ball pistons. 

1. A low-speed high-torque motor having a casing with a pintle rotatably mounting a cylinder block, said block having eight equally spaced radially extending open-ended chambers, a ball piston in each of said chambers, an annular race fixed to said casing concentric with said pintle and having a cam track with six equally spaced lobes for cycling said ball pistons in said chambers during each revolution of said cylinder block and with balance of radial forces, a series of six equally spaced pressure ports in said block for communication with the inner ends of said chambers and a series of six equally spaced outlet ports each disposed between a pair of pressure ports, a power shaft operatively connected to said cylinder block, said cam being contoured to provide a cycloidal motion for each ball piston throughout the entire revolution of said cylinder block by having a series of cycloidal curves connected one to another to provide a dwell at each lobe where a ball piston initially communicates with a pressure port and has zero acceleration and a succeeding dwell halfway between lobes where transition occurs between communication with a pressure port to communication with an outlet port and the ball piston again has zero acceleration and with said ball piston having sinusoidal acceleration between dwells whereby there is constant mechanical torque output throughout every revolution of the cylinder block, said cam track being transversely recessed to provide a cam track recess which increases the contact of each ball piston with said cam track, and said cylinder block being loosely mounted on said pintle by a radial distance exceeding an accumulation of tolerances and by an axial retainer spaced therefrom to permit rocking adjustment of said cylinder block and enable centering of the ball pistons in the cam track recess.
 2. A low-speed high-torque motor as defined in claim 1 including a sliding coupling between the power shaft and cylinder block constructed to permit movement of the cylinder block radially of the power shaft to facilitate adjustment of the cylinder block for said centering of the ball pistons. 